I’m playing BatMUD. It has a nice community and so much content (grinding included of course) that it’s still interesting after all these years. It even has its own GUI client with java scripting support, but I play with tinyfugue (a terminal client with awful scripting language).

http://www.icesus.org/Icesus/ – not sure why I like it, but I suppose it’s the interesting guild system (16 main guilds, 15 secondary guilds and dozens of others), generally good writing+world building, plus the excellent combat. There are usually 20-40 people online, about half of them at max level… It used to have 100-200 online at any time.

The players are mostly Finnish, so possibly not what most people would call friendly ;) Newbies are welcomed, though.

Tildemush. Its maturity level is closer to “proof-of-concept” than “alpha”, much less “beta”. So, I don’t really “play” it. I occasionally try to log in and try to edit my player object. Then I give feedback to the devs and quit. It’s fun watching it change over time.

I figured I’d add my own response as a comment rather than in the topic body. Right now I’m playing Realms of Despair. I like the visual descriptions and the environment, in addition to the early-level training period. It eases you into the world but still allows you to feel a part of the main city by allowing you to explore and easily return to the training grounds.

In the past I’ve played Forgotten Kingdoms. While sparsely populated, the level of detail was incredible. I left it because I wanted to experience more interaction with other mudders rather than solo play. I’ve also played GenesisMUD, which had the absolute best newbie training quest I’ve ever seen. However, the part where you lose your inventory every exit bothered me a bit too much.

I spent many hours on the Discworld MUD, though not in the last decade. I’m not overly familiar with the books from which it draws its inspiration, but I enjoyed the writing, the pretty substantial scope of the world and the friendly people I encountered there.